1. Field of the Invention
The invention relates generally to an external adapter for use with a longitudinal mode oscillographic recorder, or visicorder, as such device is sometimes designated, to expand its capabilities for recording visual traces corresponding to an incoming electrical signal. More specifically, the invention allows a longitudinal mode visicorder, designed for recording longitudinally a plurality of channels containing low frequency data to record transversely a single channel of high frequency data. Previously, two separate visicorders, one designed to operate in the longitudinal mode and the other to operate in the transverse mode, were required to make permanent visual records of both low and high frequency electrical signals.
Switching circuitry in the adapter permits the operator to select instantly either the longitudinal or transverse recording mode for the longitudinal visicorder.
The adapter also includes circuitry to record a time line reference, sweep start and sweep end indicators, and external time code data upon the visicorder graph, facilitating analysis of the recorded data.
2. Description of the Prior Art
Exemplary of a transverse, or X/Z mode oscillographic recorder is the apparatus disclosed in U.S. Pat. No. 3,434,158, issued to Stauffer et al. This patent discloses an electro-mechanical means by which a radiation emitting cathode ray tube, containing fiber optic bundles, can be driven to impress a permanent visual record of high frequency data upon a radiation sensitive recording medium. The recording medium is drawn vertically and longitudinally over the face of the cathode ray tube, while the electron beam of the cathode ray tube is driven primarily transverse to the travel of the recording medium. A single channel of incoming data is thereby recorded in parallel groups of horizontal traces (X-axis data) across the radiation sensitive medium. Variations in the intensity of the horizontal traces are known as Z-axis data, while longitudinal deviations of the traces are called Y axis data. However, owing to limited recording bandwidth of this device in the Y axis, records of high frequency data are generally recorded solely in the X and Z axes.
The Stauffer device includes a small built in monitor oscilloscope, providing immediate viewing of the input signal. However, this internal oscilloscope lacks the visual resolution and technical features necessary for proper adjustment of the oscillographic recorder's drive and control circuitry. Consequently, time consuming trial and error recording runs and adjustments are often necessary to obtain a usable record of the data stream. While this device will record a single channel of high frequency data, it does not include circuitry for isolating selective portions of the data stream for detailed analysis. These deficiencies can be overcome to some extent through the use of a larger and more sophisticated external oscilloscope, interconnected to the Stauffer visicorder in such a way as to provide control signals which synchronize the video representation of the oscilloscope with the images recorded on the visicorder. Nevertheless, even with the versatility provided by an external oscilloscope, the Stauffer visicorder cannot record multi-channel low frequency data, which is best suited for longitudinal, or Y axis mode recordation.
A plurality of simultaneously occurring low frequency signals can readily be recorded through the use of a longitudinal mode visicorder, such as the Honeywell Model 1858. This unit will record longitudinally, up to eighteen channels of time-coincident signals as parallel groups of vertical lineations along the recording medium.
However, for several reasons, the longitudinal mode visicorder is unusable to record even a single channel of high frequency data. Since the data are recorded in parallel, longitudinal channels, the longitudinal resolution of the recorded data is limited ultimately by the "pull rate", or longitudinal speed of the recording medium. Assuming that the data of interest includes pulse information, as the duration of the pulses decreases, the pull rate must increase commensurately to ensure adequate resolution of the recorded data. At pulse widths of 100.mu. seconds or less, the longitudinal recorder becomes impractical to use unless the recording medium is drawn very quickly across the face of the tube, thereby consuming a considerable amount of the expensive recording medium. However, at some point, the mechanical drive for the recording medium can no longer provide the additional speed for expanding resolution in the longitudinal axis, and adjacent longitudinal traces begin to merge.
The multi-channel recording capabilities of current longitudinal visicorders necessitate that time-share sampling methods be employed in the video drive circuitry for the fiber optics cathode ray tube. In other words, the incoming information for each channel is sampled for only a fraction of real time to determine signal presence and amplitude. For low frequency signals, the sampling rate is such that an entirely adequate representation of the information is recorded despite the fact that it is based upon time-fractional sampling methods. As the frequency of the data increases, however, information is lost during the period when other channels are being sampled, and the data as recorded are therefore incomplete.
Owing to the resolution limitations imposed by longitudinally recording data traces upon the recording medium, and the informational inaccuracy inherent in the time-sharing sampling methods, the longitudinal oscillographic recorder, or visicorder, is unable to make accurate records of high frequency data. As a consequence, to make permanent visual records of both multi-channel low frequency data as well as a single channel of high frequency data, two separate visicorders, one operating in the longitudinal mode and one operating in the transverse mode, have heretofore been required.